Evidence for the preferential disruption of moderately massive stars by supermassive black holes

TL;DR

This study uses spectral analysis of tidal disruption events to show that supermassive black holes preferentially disrupt moderately massive stars, indicating a bias towards higher mass stars in the stellar populations near SMBHs.

Contribution

It provides evidence that SMBHs tend to disrupt stars with masses around 1-2 solar masses, revealing a bias towards higher mass stars in the disruption events compared to the general stellar population.

Findings

Moderately massive stars ($ 1-2 M_\u00b0$) are preferentially disrupted.

Disruption of these stars is over-represented by a factor of  100.

Results suggest ongoing top-heavy star formation or dynamical mechanisms favoring higher mass stars near SMBHs.

Abstract

Tidal disruption events (TDEs) provide a unique opportunity to probe the stellar populations around supermassive black holes (SMBHs). By combining light curve modeling with spectral line information and knowledge about the stellar populations in the host galaxies, we are able to constrain the properties of the disrupted star for three TDEs. The TDEs in our sample have UV spectra, and measurements of the UV N III to C III line ratios enabled estimates of the nitrogen-to-carbon abundance ratios for these events. We show that the measured nitrogen line widths are consistent with originating from the disrupted stellar material dispersed by the central SMBH. We find that these nitrogen-to-carbon abundance ratios necessitate the disruption of moderately massive stars ($\gtrsim 1 - 2 M_\odot$). We determine that these moderately massive disruptions are over-represented by a factor of $\gtrsim 10^2$ when compared to the overall stellar population of the post-starburst galaxy hosts. This implies that SMBHs are preferentially disrupting higher mass stars, possibly due to ongoing top-heavy star formation in nuclear star clusters or to dynamical mechanisms that preferentially transport higher mass stars to their tidal radii.